1. Ch. 8 Notes -- Chemical Reactions
Chemical equations give information in two major areas:
1. _____________ and ______________ of the reaction.
2. Coefficients of a balanced chemical equation tell us the ______ of the substances involved.
Example of a Balanced Chemical Equation: 2H2 (g) + O2 (g)  2H2O (g)
Reactants are on the ______ side of the arrow, and the
products are on the __________ side. The arrow means “________”,
or “reacts to produce” when read aloud.
From our example, hydrogen reacts with oxygen in a ___:___ ratio.
The coefficients represent either the number of _________ or molecules present.
Reactants
products
amount
left
right
yields
2 1
moles

2. Common Symbols used in Chemical Equations
+ = used to separate 2 reactants or 2 products from each other
→ = “yields” or “reacts to produce”
= _____________ reaction (like a rechargeable battery)
(s) (l) (g) (aq) = phase of matter: (solid, liquid, gas, or “aqueous”)
= ___________ supplied to the reaction
MnO2 = a catalyst, (in this case, MnO2), is used to ________ ____ the reaction.
reversible
heat
speed up

3. Common Acids used in Chemical Equations
The formula for acids start with a ________________________.
We will learn more about the properties of acids and bases next semester.
Here is a list of common acids:
HCl ______________________
HNO3 ______________________
H2SO4 ______________________
HC2H3O2 ______________________
Hydrogen
Hydrochloric Acid
Nitric Acid
Sulfuric Acid
Acetic Acid

4. Decoding Common Chemical Equation Symbols
Practice Problems: Describe the following reactions using complete sentences.
a) NaHCO3 (s) + HCl (aq)  NaCl (aq) + H2O (l) + CO2 (g)
b) H2SO4 (aq) + BaCl2 (aq)  HCl (aq) + BaSO4 (s)
c) Write a chemical equation from the following description: “Sodium plus bromine, when heated, reacts to produce solid sodium bromide.”
Solid
sodium bicarbonate
plus
aqueous
hydrochloric acid
yields
aqueous
sodium chloride
plus
liquid water
plus
carbon dioxide gas.
Aqueous
sulfuric acid
plus
aqueous
barium chloride
yields
aqueous
hydrochloric acid
plus
solid
barium sulfate. Na
(s) +
Br2 
NaBr (s)
(l)

5. Balancing Chemical Equations
Why do you have to balance a chemical equation?
Law of Conservation of Matter (or Mass): “Matter is neither ____________ nor _______________ in chemical reactions.”
During a chemical reaction, atoms are either _________, ______________, or rearranged. The _____________ and type of each atom stays the same.
How do you balance a chemical equation?
__________________ are placed in front of the substances involved in the chemical reaction to get the same number of atoms of each element on both sides of the equation. This number will multiply the number of atoms there are in a formula.
created
destroyed
joined
separated
number
Coefficients

6. Rules for Balancing Chemical Equations
(1) Coefficients can only be placed ___ _________ of a chemical formula.
Practice Problems: How many atoms of each type are indicated in
the following compounds?
(a) 2 (NH4)3PO N= ___ H= ___ P= ___ O= ___
(b) 4 KC2H3O K= ___ C= ___ H= ___ O= ___
(c) 3 Ca(NO3) Ca= ___ N= ___ O= ___
in front 6 24 2 8 4 8 12 8 3 6 18

7. Rules for Balancing Chemical Equations
(2) You cannot change a ________________!!
Example : H O2  H2O
To balance oxygen, you cannot change water’s formula to_________!
(3) You cannot place the coefficient in the ______________ of a formula!!
Example : Al N2  AlN
To balance nitrogen, you cannot put a 2 in the middle to make _______.
(4) Reduce the coefficients to the simplest ____________ ___ ratio.
Example: H O2  4H2O can be reduced to…
__H2 + __O2  __H2O
subscript 2 2
H2O2
middle 2 2
Al2N
whole # 2 1 2

8. Rules for Balancing Chemical Equations
(5) Get rid of any ____________! Coefficients must be _________ #’s
You can’t have a _______________ of a molecule or atom!
Example: 1H ½O2  1H2O changes to…
__ H __O2  __H2O
fractions
whole
fraction
2 x ( ) 2 1 2

9. Balancing Equations: “Helpful Hints”
a) Balance elements that appear in more than one compound ________.
___(NH4)2CO3  ___NH ___CO ___H2O
b) Balance _____ “___________” as though it were one item as long as the ion stays together as a group on each side of the yields arrow.
___Al ___CuSO4  ___Al2(SO4) ___Cu
c) If you can’t seem to get it balanced, _________ _________ and begin with a different element the next time, or put a “2” somewhere and then try again.
___Li ___H2O  ___LiOH ___H2
This is what I’ll constantly be telling you to do if you are stuck and you need my help... “Pick an element to balance. How many are on the left side? How many are on the right side? ________ ____!”
___Fe(OH)3  ___Fe2O ___H2O
last 1 2 1 1
ion
chunks 2 3 1 3
start over 2 2 2 1
Fix it 2 1 3

10. Balancing Equations: “Helpful Hints”
e) Mr. Reid’s goofy “balancing song” may help:
“If there’s a ___ on the left and a ___on the right, you put a ___ on the
left and a ___ on the right, (makin’ money!)”
___Al ___O2  ___Al2O3
f) If you see only C’s H’s and O’s, balance them in this order: C, H, O.
___C2H ___O2  ___CO ___H2O 2 3 3 2 4 3 2 2 5 4 2